Crosslinked organic-inorganic hybrid membranes and their use in gas separation

ABSTRACT

The present invention is for crosslinked membranes and in particular for crosslinked poly(ethylene oxide)-cellulose acetate-silsesquioxane (PEO-CA-Si) organic-inorganic hybrid membranes and their use in gas separation. These crosslinked PEO-CA-Si membranes were prepared by in-situ sol-gel co-condensation of crosslinkable PEO-organotrialkoxysilane and CA-organotrialkoxysilane polymers in the presence of acetic acid catalyst during the formation of membranes. The crosslinkable PEO- and CA-organotrialkoxysilane polymers were synthesized via the reaction between the hydroxyl groups on PEO (or on CA) and the isocyanate on organotrialkoxysilane to form urethane linkages under mild conditions. The crosslinked PEO-CA-Si membranes exhibited both increased selectivity of CO 2 /N 2  and CO 2  permeability as compared to a CA membrane, suggesting that these membranes are very promising for gas separations such as CO 2 /N 2  separation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of copending application Ser. No.12/131,392 filed Jun. 2, 2008, the contents of which are herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention pertains to crosslinked organic-inorganic hybridmembranes. More specifically, this invention pertains to crosslinkedpoly(ethylene oxide)-cellulose acetate-silsesquioxane (PEO-CA-Si)organic-inorganic hybrid membranes and methods of making thesemembranes. This invention also pertains to the application of thesemembranes for gas separations such as CO₂/N₂ separation.

CO₂ is an impurity that must be removed from mixtures with light gasessuch as CH₄, N₂ and H₂, and the scale of these separations is enormous.See Kohl, et al., GAS PURIFICATION, Fifth Ed., Gulf Publishing, Houston,Tex., 1997. Membrane-based separation of CO₂ from gas streams is animportant unit operation. Separations of CO₂ with membranes includenatural gas purification, CO₂ capture from flue gas (primarily inmixtures with N₂), and metabolic CO₂ removal from space life-supportingsystems (extravehicular mobility unit (EMU), space shuttle or spacestation), and CO₂ removal from H₂.

General public awareness concerning the atmospheric greenhouse or“greenhouse warming” effect attributed to CO₂ has created the need todevise environmentally friendly and energy efficient technologies forthe removal of CO₂ from industrial waste gas streams. Flue gas fromfossil fuel power generation (primarily in mixtures with N₂) is thelargest single contributor to CO₂ emissions. Therefore, CO₂ recoveryfrom flue gas is becoming more important due to global warming.Generally, flue gas has a large volume and a relatively lowconcentration in CO₂ (typically 10-20 mol-%). Membrane-based separationof CO₂ from flue gas holds great promise due to its low energyconsumption, low cost, easy operation, and low maintenance. A membranesystem with a high processing capacity and a reasonably high selectivityfor CO₂/N₂ is required in order to compete with other separationtechniques such as physical or chemical absorption, low temperaturedistillation and pressure swing adsorption.

Separation of CO₂ from flue gas (mainly N₂) with commonly used polymericmembranes (e.g. cellulose acetate and fluorine-containing polyimides) orinorganic membranes (e.g. zeolite, sol-gel silica or carbon molecularsieve) is achieved by differences in diffusion rates and/or adsorptionstrengths of mixture components in the polymer matrix or the inorganicmembrane pores, and selectivity is usually rather low, e.g.approximately 20 for CO₂/N₂ at about 50° C. for gas mixtures. See Baker,IND. ENG. CHEM. RES., 41: 1393 (2002); Tsai, et al., J. MEMBR. SCI, 169:255 (2000). On the other hand, facilitated transports of CO₂ inion-exchange or immobilized liquid membranes have been intensivelyinvestigated because they have high selectivity due to the chemicalinteraction between CO₂ and carrier molecules. See Baltus, et al., SEP.SCI. TECH., 40: 525 (2005). For example, a number of recently developedimmobilized liquid membranes exhibited high (>1000) CO₂/N₂ selectivitydue to facilitated CO₂ transport mechanism. However, there are still nopractical applications for this type of membranes mainly because theirCO₂ permeation rate is rather low especially at moderate levels ofrelative humidity (<40%), and also the durability and retention of theliquid in real process conditions are poor. See Kovvali, et al., IND.ENG. CHEM. RES., 40: 2502 (2001); Kovvali, et al., IND. ENG. CHEM. RES.,41: 2287 (2002).

Polymer blends have been the focus of extensive gas membrane separationresearch since 1980's. For example, poly(ethylene glycol) (PEG) andcellulose acetate or cellulose nitrate blend membranes have beeninvestigated for CO₂/N₂ separation. It has been reported that PEG candissolve substantial amounts of sour gases such as CO₂, and thediffusivity of large penetrants such as CO₂ and CH₄ in PEG may be high,considering its flexible main chain. A miscible blend membranecontaining 10 wt-% of PEG with molecular weight of 20,000 showed bothhigher CO₂/N₂ selectivity and CO₂ permeability than those of thecellulose acetate membrane. See Li, et al., J. APPL. POLYM. SCI., 58:1455 (1995). These blend polymers containing PEG, however, still haveissues of durability and retention of the liquid PEG for real industrialapplications.

To solve the longer term stability problem of PEG (or poly(ethyleneoxide), PEO)-based polymer membranes, various techniques have beenreported to crosslink PEG or PEO. For instance, radiation or radicalcrosslinking of PEG or PEO has been reported. Crosslinking by reactionsof end groups such as hydroxyl or vinyl groups has been studied. See Linet al., J. MOL. STR., 739: 57 (2005); Lin, et al., MACROMOLECULES, 38:8394 (2005); Lin, et al., MACROMOLECULES, 38: 8381 (2005). All of thesecrosslinked PEG- or PEO-based membranes are organic polymeric membraneswithout the presence of inorganic segments, therefore, issues related tochemical resistance, thermal stability, and pressure stability (e.g.plasticization or swelling of membrane) may still exist. In addition,this type of crosslinked organic polymeric membranes has never beenfabricated into asymmetric hollow fiber or flat sheet membranes possiblybecause they cannot be easily integrated into current polymer membranemanufacturing process using phase-inversion technique.

SUMMARY OF THE INVENTION

In order to overcome the inherent disadvantages of the existingmembranes and to enhance gas separation performance, this inventionprovides for crosslinked organic-inorganic hybrid membranes withinterchain-connected cellulose acetate and poly(ethylene oxide) organicpolymers through covalently bound inorganic silsesquioxane ligands.

In general, the invention provides for crosslinked organic-inorganichybrid membranes. More specifically, the present invention involves thepreparation of crosslinked poly(ethylene oxide)-celluloseacetate-silsesquioxane (PEO-CA-Si) organic-inorganic hybrid membranescontaining covalent bonds between the cellulose acetate (CA) and thepoly(ethylene oxide) (PEO) polymer chains and their application for gasseparations such as separation of carbon dioxide and nitrogen. Thesecrosslinked PEO-CA-Si membranes with covalentlyinterpolymer-chain-connected hybrid networks were prepared by simplein-situ sol-gel co-condensation of crosslinkablePEO-organotrialkoxysilane and CA-organotrialkoxysilane polymers in thepresence of acetic acid catalyst during the formation of membranes. Thecrosslinkable PEO- and CA-organotrialkoxysilane polymers are synthesizedvia the reaction between the hydroxyl groups on PEO (or on CA) and theisocyanate on organotrialkoxysilane to form a urethane linkage undermild conditions.

These crosslinked organic-inorganic hybrid polymer membranes providefavorable characteristics including the following: First, the hardcellulose acetate and inorganic silsesquioxane segments provide goodmechanical strength, the inorganic silsesquioxane crosslinking segmentsalso offer good chemical resistance, high thermal and pressurestabilities, and the soft PEO segments offer high permeability becauseof the high mobility for polyether chains. Second, the strong affinityof the PEO segments for CO₂ molecules is believed to result in the highCO₂/N₂ selectivity. Third, the degree of crosslinking for thecrosslinked organic-inorganic hybrid membranes can be easily controlledby adjusting the ratio of precursor organic CA and PEO polymers and theorganosilicon alkoxide crosslinking agent. Fourth, these crosslinkedorganic-inorganic hybrid polymer membranes are different fromorganic-inorganic hybrid mixed matrix membranes in that there is noinorganic particle size issue, and they have much better chemical andmechanical stabilities compared to organic-inorganic hybrid mixed matrixmembranes due to the existence of covalent bonds between the organic andinorganic segments; Fifth, the crosslinked PEO-CA-Si membranes in thisinvention can be easily integrated into current CA polymer membranemanufacturing process due to their simplified synthetic procedurecompared to the crosslinked PEO dense film prepared by free radicalpolymerization method in the literature.

The crosslinked PEO-CA-Si membranes exhibited both significantlyenhanced permeability of CO₂ (increased up to 60%) and greatly improvedselectivity of CO₂/N₂ (increased up to 30%) compared to a celluloseacetate membrane. This improved selectivity means that these membranesare very promising for gas separations such as CO₂/N₂, olefin/paraffin,aromatics/non-aromatics, polar molecules such as H₂O, H₂S, SO₂ andNH₃/mixtures with CH₄, N₂, H₂, air, and other light gases separations.

DETAILED DESCRIPTION OF THE INVENTION

In recent years, numerous efforts have been focused on design ofpolymers containing poly(ethylene glycol) (PEG) or poly(ethylene oxide)(PEO) segments for CO₂/N₂ and CO₂/H₂ separations mainly because of theunique properties of the polar ether oxygen in PEG or PEO for CO₂separations. However, the low molecular weight PEOs are in liquid phaseand the solid-state high molecular weight PEOs are subject to a strongtendency to crystallize, which are deleterious conditions for gaspermeability.

Crosslinking is a useful technique to convert liquid-state low molecularweight PEO to solid-state PEO and to reduce crystallinity in highmolecular weight PEO. Crosslinking is also a useful method to improvethe gas separation performance of polymer membranes. Crosslinking ofpolymers can provide crosslinked polymers with higher T_(g) thanun-crosslinked polymers. Therefore, the crosslinked polymer membranesalways have a high resistance to plasticization, and exhibit excellentthermal and chemical stability, enhanced selectivity of gas pairs,improved mechanical stability, or enhanced contaminant resistance thanthe uncrosslinked polymer membranes. The membrane crosslinking methodsinclude thermal treatment, radiation, chemical crosslinking,UV-photochemical, blending with other polymers, etc. See Koros, et al.,US 20030221559 (2003); Jorgensen, et al., US 2004261616 (2004); Patel,et al., ADV. FUNC. MATER., 14 (7): 699 (2004); Patel, et al., MACROMOL.CHEM. PITY., 205: 2409 (2004).

There has been only a little work that has focused on crosslinking ofpolymeric membranes using inorganic materials. This invention pertainsto crosslinked organic-inorganic hybrid membranes. More specifically,this invention pertains to crosslinked poly(ethylene oxide)-celluloseacetate-silsesquioxane (PEO-CA-Si) organic-inorganic hybrid membranesand methods of making the same. This invention also pertains to theapplication of these crosslinked poly(ethylene oxide)-celluloseacetate-silsesquioxane (PEO-CA-Si) organic-inorganic hybrid membranesfor gas separations such as the CO₂/N₂ separation.

The crosslinked PEO-CA-Si organic-inorganic hybrid membranes wereprepared by in-situ sol-gel co-condensation of crosslinkablePEO-organotrialkoxysilane and CA-organotrialkoxysilane polymers in thepresence of acetic acid catalyst during the formation of the membranes.The crosslinked PEO-CA-Si organic-inorganic hybrid membranes can also beprepared from crosslinkable polypropylene oxide-ethylene oxide-propyleneoxide) (PPO-PEO-PPO tri-block co-polymer containing PEOsegment)-organotrialkoxysilane and CA-organotrialkoxysilane polymers inthe presence of acetic acid catalyst during the formation of themembranes. The crosslinkable PEO- and CA-organotrialkoxysilane polymerswere synthesized via the reaction between the hydroxyl groups on PEO(the molecular weight of PEO can be varied, e.g. PEO400 and PEO1500 withmolecular weights (M_(n)) of 400 and 1500, respectively) or CA and theisocyanate on the organotrialkoxysilane to form urethane linkages undermild conditions. All kinds of PEO polymers with different molecularweights in liquid or solid state can be used for the preparation of thisnew type of crosslinked organic-inorganic hybrid membranes. In addition,PPO-PEO-PPO tri-block co-polymer with different molecular weights (e.g.PPO-PEO-PPO2000 with M_(n)=2000) can also be used for the preparation ofthis new type of crosslinked organic-inorganic hybrid membranes. Thecrosslinkable PPO-PEO-PPO-organotrialkoxysilane polymers can be preparedvia the reaction between the amino groups on both ends of PPO-PEO-PPOtri-block co-polymer and the epoxy group on the organotrialkoxysilane toform imine linkage under mild reaction conditions. Subsequent in-situhydrolysis and condensation of these crosslinkable precursor polymersduring the membrane-forming process yielded crosslinkedorganic-inorganic hybrid polymer membranes with covalentlyinterpolymer-chain-connected hybrid networks.

The crosslinkable precursor polymers are prepared by reaction of theprecursor polymer such as polyethylene oxide with an organosiliconalkoxide in the presence of a solvent such as tetrahydrofuran. Thecrosslinked organic-inorganic polymers are made by the sol-gelpolymerization of two or more of these crosslinkable precursor polymerswhich may be solution cast as a dense film or otherwise used as amembrane.

Typical polymers as the precursor organic polymer suitable for thepreparation of crosslinked organic-inorganic hybrid polymer membranescan be selected from any rubbery or glassy polymers containing organicfunctional groups on terminals or on the side chains of the polymerbackbones (or called macromolecular backbones). The organic functionalgroups on the precursor organic polymer can be hydroxyl, amino, epoxy,isocyanato, dianhydride, etc.

Example precursor organic polymers include poly(ethylene oxide)s (PEO),cellulose acetates (CA), poly(propylene oxide)s (PPO),co-block-poly(ethylene oxide)-poly(propylene oxide)s (PEO-PPO),tri-block-poly(propylene oxide)-poly(ethylene oxide)-poly(propyleneoxide)s (PPO-PEO-PPO), poly(propylene glycol)-block-poly(ethyleneglycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (PAPE),dendritic PEO, and hyperbranched amine-terminated PEO.

The organosilicon alkoxide crosslinking agents used to form covalentbonds with the precursor organic polymer should have twocharacteristics. One is that these organosilicon alkoxide crosslinkingagents should contain at least one organic functional group that canreact with the organic functional groups on the precursor organicpolymer. The other is that these organosilicon alkoxide crosslinkingagents should have at least two silicon alkoxide groups that cancrosslinked with each other via a sol-gel condensation polymerization toform a fully crosslinked inter-polymer-chain network.

In the structure for the organosilicon alkoxide, n=−2−10; m=3; R′ is anorganic functional group which may include of —(CH₂)_(a)NH₂ (a=1−20),—(CH₂)_(a)OH (a=1−20), —(CH₂)_(a)NH(CH₂)₂NH₂ (a=1−20),OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, —CH₂)_(a)N═C═O(a=1−20), —(CH₂)_(a)CH(O)CH₂(a=1−20), and mixtures thereof; R″ is a C1-C8 hydrocarbon group.

The crosslinking catalysts used to catalyze the sol-gel polymerizationcan be selected from either bases or acids. More preferably, thecrosslinking catalysts are selected from weak acids such as acetic acidor hydrochloric acid.

The successful formation of urethane linkages between organic PEO and CApolymers and the inorganic silsesquioxane segments were confirmed byFTIR spectra. The crosslinked CA-silsesquioxane membrane showed theappearance of a vibration band at about 1568 cm⁻¹ corresponding to NH—COgroup, indicating the formation of urethane linkages.

In this invention, crosslinked PEO-CA-Si organic-inorganic hybridmembranes were prepared that exhibited the advantages of the organic PEOpolyether segments and CA polymer matrix, as well as the advancedfeatures of inorganic silsesquioxane crosslinking segments. Ten to fiftypercent by weight of the crosslinkable PEO-organotrialkoxysilanepolymers were added to crosslinkable CA-organotrialkoxysilane polymers.

The permeability (P) and ideal selectivity (α_(CO2/N2)) of thecrosslinked PEO-CA-Si organic-inorganic hybrid membranes were measuredby pure gas measurements at 50° C. under approximately 690 kPa (100psig) pressure. As shown in Table 1, the crosslinked PEO-CA-Siorganic-inorganic hybrid membranes offer both enhanced P_(CO2) andα_(CO2/N2) compared to those of the pure CA polymer membrane, suggestingthis new type of crosslinked PEO-CA-Si organic-inorganic hybridmembranes is very promising for gas separation applications of such asfor CO₂ removal from flue gas (mainly N₂).

For example, as shown in Table 1, the P_(CO2) of crosslinked 30%PPO-PE0-PPO2000-CA-Si with 30 wt-% of PPO-PEO-PPO2000-Si segments (12.2Barrer) increased approximately 60% over that of pure CA dense film(7.56 Barrer), and in the meantime the α_(CO2/N2) (29.8) increasedapproximately 25% compared to that of pure CA dense film(α_(CO2)N₂=23.7). For another example, the P_(CO2) of crosslinked 30%PEO400-CA-Si with 30 wt-% of PEO400—Si segments (10.6 Barrer) increasedapproximately 40% over that of pure CA dense film (7.56 Barrer), and inthe meantime the α_(CO2/N2) (31.1) increased approximately 30% comparedto that of pure CA dense film (α_(CO2/N2)=23.7).

Pure gas permeation results for the crosslinked PEO-CA-Siorganic-inorganic hybrid membranes in this invention (Table 1) werecompared with those of the CA-PEG uncrosslinked blend membranes reportedin the literature (Table 2, see Li, et al., J. APPL. POLYM. Su., 58:1455 (1995)). It can been seen from Table 2 that the uncrosslinked blendCA-PEG membranes containing 10 wt-% of PEG200, PEG600, and PEG2000 withPEG molecular weights of 200, 600, and 2000, respectively, showed verypoor CO₂/N₂ selectivity of less than 15 without improvement for CO₂permeability compared to pure CA membrane. While as shown in Table 1,the crosslinked PEO-CA-Si membranes prepared by chemical crosslinkingapproach described in this invention containing 30 wt-% of PEO400,PEG1500, or PPO-PEO-PPO2000 with molecular weights of 400, 1500, and2000, respectively, exhibited both greatly improved CO₂/N₂ selectivitiesand CO₂ permeability compared to the pure CA membrane. These resultsdemonstrated the effectiveness of the chemical crosslinking approach toimprove the CO₂/N₂ gas separation performance of CA-PEO blend membranes.

The crosslinked organic-inorganic hybrid polymer membranes described inthis invention can be used for a variety of liquid and gas separationssuch as CO₂/N₂, olefin/paraffin, aromatics/non-aromatics, polarmolecules such as H₂O, H₂₅, SO₂, and NH₃/mixtures with CH₄, N₂, H₂, air,and other light gas separations.

TABLE 1 Pure gas permeation test results of CA and crosslinked PEO-CA-Simembranes ^(a) Crosslinked 30% Crosslinked 30% Crosslinked 30%PPO-PEO-CA- Film Pure CA PEO400-CA-Si PEO1500-CA-Si PPO2000-Si P_(CO) ₂(Barrer) 7.56 10.6 10.4 12.2 ΔP_(CO) ₂ (Barrer) 0 40.2% 37.6% 61.4%P_(N) ₂ (Barrer) 0.319 0.341 0.362 0.410 α_(CO) ₂ _(/N) ₂ 23.7 31.1 28.729.8 Δα_(CO) ₂ _(/N) ₂ 0 31.2% 21.1% 25.7% P_(CH) ₄ (Barrer) 0.321 0.5250.548 0.649 α_(CO) ₂ _(/CH) ₄ 23.6 20.2 19.0 18.7 ^(a) Tested at 50° C.under 690 kPa (100 psig). 1 Barrer = 10⁻¹⁰ cm³(STP) · cm/cm² · sec ·cmHg.

TABLE 2 Pure gas permeation test results of CA and its blend membranescontaining PEG^(a) CA + 10% CA + 10% CA + 10% CA + 10% CA + 10% Film CAPEG200 PEG600 PEG2000 PEG6000 PEG20000 P_(CO) ₂ _((Barrer)) 5.96 4.925.72 6.30 6.16 7.49 P_(N) ₂ _((Barrer)) 0.231 0.918 0.418 0.452 0.1940.207 P_(CH) ₄ _((Barrer)) 0.205 1.14 0.831 0.549 0.247 0.248 P_(O) ₂_((Barrer)) 1.05 1.46 1.22 1.10 — 0.993 P_(H) ₂ _((Barrer)) 14.9 22.214.8 13.8 10.9 11.4 D_(CO) ₂ 0.560 0.475 0.639 0.723 0.929 1.00 (×10⁸cm²/sec) S_(CO) ₂ 106 104 89.5 80.4 66.3 74.6 (×10³ cm³(STP)/cm³.cmHg)α_(CO) ₂ _(/N) ₂ 25.8 5.36 13.7 13.9 31.7 36.2 α_(CO) ₂ _(/CH) ₄ 29.24.31 6.88 11.5 25.0 30.3 ^(a)Tested at 35° C. under 27 kPa (3.9 psig);Table from literature Li, et al., J. APPL. POLYM. SCI., 58: 1455 (1995).1 Barrer = 10⁻¹⁰ cm³(STP) · cm/cm² · sec · cmHg.

Example 1 Synthesis of Crosslinkable Cellulose Acetate(CA)-Organotriethoxysilane Hybrid Polymer

5.0 g (18.9 mmol) of CA polymer was dissolved in 100.0 g of THF or1,4-dioxane solvent. 1.29 g (5.2 mmol) of3-isocyanatopropyltriethoxysilane was added to the CA solution. Afterthe solution was heated at 60° C. for 24 hours, the crosslinkableCA-organotriethoxysilane hybrid polymer solution was obtained.

Example 2 Synthesis of Crosslinkable PEO-Organotriethoxysilane HybridPolymers

The crosslinkable PEO-organotriethoxysilane hybrid polymers weresynthesized from the reaction between PEO400 (M_(n)=400) or PE01500(M_(n)=1500) polymer and 3-isocyanatopropyltriethoxysilane with PEO400(or PE01500) to 3-isocyanatopropyltriethox-ysilane molar ratio of 1:2using the same procedure as described in Example 1.

Example 3 Synthesis of Crosslinkable PPO-PEO-PPO-OrganotriethoxysilaneHybrid Polymer

The crosslinkable PPO-PEO-PPO-organotriethoxysilane was synthesized fromthe reaction between poly(propylene glycol)-block-poly(ethyleneglycol)-block-poly(propylene glycol) bis(2-aminopropyl ether)(PPO-PEO-PPO with M_(n)=2000) and (3-glycidoxypropyl) trimethoxysilanewith PPO-PEO-PPO to (3-glycidoxypropyl)trimethoxysilane molar ratio of1:2 according to the same procedure as that for the crosslinkableCA-organotriethoxysilane except that the reaction was conducted at roomtemperature.

Example 4 Preparation of Crosslinked PEO-CA-Si Organic-Inorganic HybridPolymer Membranes

A catalytic amount of acetic acid (0.01 g, 0.17 mmol) was added to 18.38g of a polymer solution in 1,4-dioxane or THF containing 0.708 g (2.13mmol) of crosslinkable CA-organotriethoxysilane prepared in Example 1and 0.212 g of PEO400-organotriethoxysilane polymer (orPEO1500-organotriethoxysilane polymer) prepared in Example 2 followed bythe addition of 0.01 g (0.22 mmol) of ethanol. The resulting solutionwas mixed for at least 6 hours at room temperature. The solution wasthen filtered through a 0.2 μm PTFE membrane filter. 16 g of thefiltrate solution containing about 0.8 g of total polymers was cast ontothe surface of a clean glass plate, and dried at room temperature for 24hours. The resulting crosslinked PEO-CA-Si hybrid polymer membrane wasdetached from the glass plate and further dried at 110° C. for at least48 hours in vacuo.

Example 5 Preparation of Crosslinked PPO-PEO-PPO-CA-Si Organic-InorganicHybrid Polymer Membranes

A catalytic amount of acetic acid 0.01 g, 0.17 mmol) was added to 18.38g of a polymer solution in 1,4-dioxane or THF containing 0.708 g (2.13mmol) of crosslinkable CA-organotriethoxysilane prepared in Example 1and 0.212 g (0.085 mmol) of PPO-PEO-PPO-organotriethoxysilane polymerprepared in Example 3 followed by the addition of 0.01 g, 0.17 mmol) ofethanol. The resulting solution was mixed for at least 6 hours at roomtemperature. The solution was then filtered through a 0.2 μm PTFEmembrane filter. 16.0 g of the filtrate solution containing about 0.8 gof total polymers was cast onto the surface of a clean glass plate, anddried at room temperature for 24 hours. The resulting crosslinkedPPO-PEO-PPO-CA-Si hybrid polymer membrane was detached from the glassplate and further dried at 110° C. for at least 48 hours in vacuo.

1. A process for separating at least one gas from a mixture of gases,the process comprising: a) providing a crosslinked organic-inorganichybrid polymer membrane comprising a crosslinked organic-inorganichybrid polymer made from at least two different precursor organicpolymers having hydroxyl, amino, epoxy, isocyanato, or dianhydridegroups wherein said precursor organic polymer is selected from the groupconsisting of poly(ethylene oxide) (PEO), cellulose acetate (CA),poly(propylene oxide) (PPO), co-block-poly(ethyleneoxide)-poly(propylene oxide) (PEO-PPO), tri-block-poly(propyleneoxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO),poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propyleneglycol) bis(2-aminepropyl ether) (PAPE), dendritic PEO, andhyperbranched amine-terminated PEO, and crosslinked with anorganosilicon alkoxide crosslinking agent; and b) contacting the mixtureof gases to a first side of the crosslinked organic-inorganic hybridpolymer membrane to cause said at least one gas to permeate the mixedmatrix membrane; and c) removing from a second side of the membrane apermeate gas composition comprising at least a portion of said at leastone gas which permeated said membrane.
 2. The process of claim 1 whereinsaid precursor organic polymer is selected from the group consisting ofpoly(ethylene oxide) (PEO), cellulose acetate (CA), poly(propyleneoxide) (PPO), co-block-poly(ethylene oxide)-poly(propylene oxide)(PEO-PPO), tri-block-poly(propylene oxide)-poly(ethyleneoxide)-poly(propylene oxide) (PPO-PEO-PPO), poly(propyleneglycol)-block-poly(ethylene glycol)-block-poly(propylene glycol)bis(2-aminepropyl ether) (PAPE), dendritic PEO, and hyperbranchedamine-terminated PEO.
 3. The process of claim 2 wherein one of saidprecursor polymers is cellulose acetate.
 4. The process of claim 1wherein said organosilicon alkoxide crosslinking agent comprises

wherein n=−2-10; m=3; R′ is an organic functional group selected fromthe group consisting of —(CH₂)_(a)NH₂, —(CH₂)_(a)OH,—(CH₂)_(a)NH(CH₂)₂NH₂, OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, —(CH₂)_(a)N═C═O,—(CH₂)_(a)CH(O)CH₂, and mixtures thereof wherein a=1-20; and wherein R″is a C₁-C₈ hydrocarbon group.
 5. The process of claim 1 wherein one ofsaid precursor polymers is cellulose acetate and at least one of saidprecursor polymers is selected from the group consisting ofpoly(ethylene oxide) (PEO), poly(propylene oxide) (PPO),co-block-poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO),tri-block-poly(propylene oxide)-poly(ethylene oxide)-poly(propyleneoxide) (PPO-PEO-PPO), poly(propylene glycol)-block-poly(ethyleneglycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (PAPE),dendritic PEO, and hyperbranched amine-terminated PEO.
 6. The process ofclaim 5 wherein one of said precursor polymers is cellulose acetate andat least two of said precursor polymers are selected from the groupconsisting of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO),co-block-poly(ethylene oxide)-poly(propylene oxide)s (PEO-PPO),tri-block-poly(propylene oxide)-poly(ethylene oxide)-poly(propyleneoxide) (PPO-PEO-PPO), poly(propylene glycol)-block-poly(ethyleneglycol)-block-poly(propylene glycol) bis(2-aminepropyl ether) (PAPE),dendritic PEO, and hyperbranched amine-terminated PEO.
 7. The process ofclaim 2 wherein one of said precursor polymers is cellulose acetate andone of said precursor polymers is poly(ethylene oxide).
 8. The processof claim 1 wherein said crosslinked organic-inorganic hybrid polymermembrane comprises a crosslinked poly(ethylene oxide)-celluloseacetate-silsesquioxane organic-inorganic hybrid polymer.
 9. The processof claim 1 wherein said mixture of gases is selected from the groupconsisting of carbon dioxide and nitrogen; olefins and paraffins; carbondioxide and methane; aromatics and non-aromatics; water and methane;sulfur dioxide and nitrogen, hydrogen sulfide and methane; ammonia andmethane; hydrogen sulfide and nitrogen; hydrogen sulfide and hydrogen,oxygenates and hydrocarbon, nitrogenates and hydrocarbon, and sulfurcompounds and hydrocarbon.
 10. The process of claim 1 wherein saidmixture of gases is selected from the group consisting of carbondioxide/methane, carbon dioxide/nitrogen, olefin/paraffin,aromatics/non-aromatics, water, hydrogen sulfide, sulfur dioxide, andammonia mixtures with methane, nitrogen, hydrogen and air.
 11. Theprocess of claim 10 wherein said mixtures of gases comprises carbondioxide and nitrogen.
 12. The process of claim 10 wherein said mixturesof gases comprises carbon dioxide and methane.